1. Technical Field
The present invention relates to high strength structural panels useful for mine safe rooms, that is, chambers within mines where miners can retreat in an emergency, and where food, supplies, stores of oxygen, etc. are maintained. More particularly, the present invention relates to the use of carbon foam in structural insulated panels which are highly resistant to heat, moisture, and other environmental stresses while maintaining an extremely high compressive strength, thus providing a safe haven for trapped miners.
2. Background Art
Mine safety is becoming an increasingly important topic, especially as explosions and other emergency events have taken the lives of miners. One suggested safety measure for miners in the event of an emergency is the provision of so-called mine safe rooms. Mine safe rooms are structures within mines to which miners can retreat in the event an emergency or other situation prevents the miners from escaping to the surface. Mine safe rooms are sealed off from toxic gases which may collect after a fire or explosion, usually contain communications means, and are stocked with supplies, such as food, water and oxygen, to provide a safe haven for miners while they await rescue.
Current mine safe room technology has the walls of the safe room constructed of steel or other metal. While steel can provide blast protection, shielding miners from explosions, steel can do little to protect the miners from the heat generated by an explosion or resulting fire. Indeed, in the event of fire, mine safe rooms formed of steel can exacerbate the situation, because of the thermal conductivity of steel. Thus, the present invention relates to the formation of mine safe rooms using structural insulated panels which comprise carbon foam. While structural insulated panels (referred to in the industry as SIPs) are known, forming SIPs with a carbon foam core is not.
In Hardcastle et al. (U.S. Pat. No. 4,425,396) an insulating panel is disclosed with a synthetic organic polymeric foam with protective weathering layers comprised of multiple thermoplastic sheets.
Cahill (U.S. Pat. No. 6,656,858) describes a lightweight laminate wall comprised of a low density layer of from about 0.5 to 3 pounds per cubic foot and a second, reinforcing layer of a polymeric fabric. These structures are lightweight, have a low moisture resistance and meet building code requirements regarding transverse wind loading.
Porter (U.S. Pat. No. 6,599,621) describes a SIP with high strength and resistance to fire and particularly to water and changes in humidity. The disclosed structures are comprised of an inner insulating core with a gypsum fiberboard on one face of the insulating core and an oriented strand board on the second face of the insulating core. Preferably, the insulating core is comprised of a plastic foam such as expanded polystyrene or urethane which is bonded to both the gypsum fiberboard and the oriented strand board.
Porter (U.S. Pat. No. 6,588,172) describes the incorporation of a laminated layer of plastic impregnated paper into a SIP to increase the panel's tensile strength while rendering it impervious to moisture. This layer is typically situated between the gypsum board and plastic foam core, adhered through a conventional bonding agent.
Parker (U.S. Pat. No. 4,628,650) describes a SIP with a foam core with a layer having an overhang projecting from the foam core edges. The overhang is situated to facilitate an effective seal between adjacent SIPs, providing better thermal insulation. Additionally, the core of the panels has channels through the structure for the placement of joists, studs or rafters.
Clear (U.S. Pat. No. 6,079,175) describes a SIP of cementitious material for building structures. A lightweight fill material such as bottom ash, cement and water is poured between spaces of two outermost ribs, which is claimed to provide insulation, strength and also rigidity to the panel and therefore the structure the panel comprises. This SIP has the advantage of being constructed in remote or more barren areas as it is fairly inexpensive to create.
Pease (U.S. Pat. No. 6,725,616) prepares an insulated concrete wall either cast or built with blocks which is attached to reinforced insulated strips. The patentee indicates that users will require less time and labor in making insulated using the patentee's method of fixing reinforced rigid foam to the surface of a concrete wall.
Pease (U.S. Pat. No. 6,892,507) describes a method and apparatus for making an SIP with a rigid foam sheet. The rigid foam sheets have multiple grooves in which reinforcing strips are situated. The strips and rigid foam are then covered and bonded with a reinforcing sheet, the sheet providing both structural support and moisture retention.
Unfortunately, SIPs produced by the prior art are not effective for the formation of mine safe rooms, as lacking high strength including high compressive strength values. Furthermore, and more importantly, most conventional SIPs are not effective against high heat or open flames, either combusting or experiencing significant charring. In addition, the prior art SIPs generally lack a high strength to density ratio, making such SIPs ill suited for applications where a lightweight, insulating, yet strong panel is necessary for a safe room within a mine.
What is desired, therefore, is structural panel which is of a low density and has desirable thermal insulating properties, where the panel has a high strength and high strength to density ratio, and relatively non-combustible, and therefore useful for the construction of mine safe rooms. Indeed, a combination of characteristics, including strength to density ratios and compressive strength higher than contemplated in the prior art, as well as fire retardancy higher than contemplated in the prior art, have been found to be necessary for mine safe room structural applications.